1. Field of the Invention
The present invention is directed to the field of rolled fingerprint capture, and more specifically, to capturing and combining multiple fingerprint images to generate an overall rolled fingerprint image.
2. Related Art
A rolled fingerprint scanner is a device used to capture rolled fingerprint images. The scanner captures the image of a user""s fingerprint as the user rolls a finger across an image capturing surface. Multiple fingerprint images may be captured by the scanner as the finger is rolled. These images may be combined to form a composite rolled fingerprint image. A computer system may be used to create the composite rolled fingerprint image. Fingerprint images captured by a digital camera are generally comprised of pixels. Combining the pixels of fingerprint images into a composite fingerprint image is commonly referred to as pixel xe2x80x9cknitting.xe2x80x9d
The captured composite rolled fingerprint image may be used to identify the user. Fingerprint biometrics are largely regarded as an accurate method of identification and verification. A biometric is a unique, measurable characteristic or trait of a human being for automatically recognizing or verifying identity. See, e.g., Roethenbaugh, G. Ed., Biometrics Explained (International Computer Security Association: Carlisle, Pa. 1998), pages 1-34, which is herein incorporated by reference in its entirety.
Capturing rolled fingerprints using a fingerprint scanner coupled to a computer may be accomplished in a number of ways. Many current technologies implement a guide to assist the user. These guides primarily come in two varieties. The first type includes a guide located on the fingerprint scanner itself. This type may include guides such as light emitting diodes (LEDs) that move across the top and/or bottom of the scanner. The user is instructed to roll the finger at the same speed as the LEDs moving across the scanner. In doing so, the user inevitably goes too fast or too slow, resulting in poor quality images. The second type includes a guide located on a computer screen. Again, the user must match the speed of the guide, with the accompanying disadvantages. What is needed is a method and apparatus for capturing rolled fingerprint images without the requirement of a guide.
Current devices exist for collecting rolled fingerprint images. For instance, U.S. Pat. No. 4,933,976 describes using the statistical variance between successive fingerprint image xe2x80x9cslicesxe2x80x9d to knit together a composite fingerprint image. This patent also describes techniques for averaging successive slices into the composite image. These techniques have the disadvantage of less than desirable image contrast. What is needed is a method and apparatus for capturing rolled fingerprint images with improved contrast imaging.
The present invention is directed to a method and apparatus for rolled fingerprint capture. The invention detects the start of a fingerprint roll. A plurality of fingerprint image frames are captured. A centroid window corresponding to each of the plurality of captured fingerprint image frames is determined. Pixels of each determined centroid window are knitted into a composite fingerprint image. The end of the fingerprint roll is detected.
In an embodiment, a pixel intensity difference count percentage value between a current fingerprint image frame and a previous fingerprint image frame is generated. Whether the generated pixel intensity difference count percentage value is greater than a start roll sensitivity threshold percentage value is determined.
Furthermore, in embodiments, a pixel window in a captured fingerprint image frame is determined. A leading edge column and a trailing edge column of a fingerprint image in the corresponding generated pixel window are found. A centroid window in the captured fingerprint image frame bounded by the leading edge column found and the trailing edge column found is generated.
The present invention further provides a novel algorithm for knitting fingerprint images together. Instead of averaging successive pixels, the algorithm of the present invention compares an existing pixel value to a captured potential new pixel value. New pixel values are only knitted if they are darker than the existing pixel value. The resultant image of the present invention has a much higher contrast than images that have been averaged or smoothed by previous techniques. In an embodiment, the invention compares the intensity of each pixel of the determined centroid window to the intensity of a corresponding pixel of a composite fingerprint image. The pixel of the composite fingerprint image is replaced with the corresponding pixel of the determined centroid window if the pixel of the determined centroid window is darker than the corresponding pixel of the composite fingerprint image.
Furthermore, existing fingerprint capturing devices require actuating a foot pedal to begin the capture process. The present invention requires no such activation. The algorithm of the present invention can be instantiated through a variety of software/hardware means (e.g. mouse click, voice command, etc.).
According to a further feature, the present invention provides a rolled fingerprint capture algorithm that can operate in either of two modes: guided and unguided. The present invention may provide the guided feature in order to support legacy systems; however, the preferred mode of operation is the unguided mode. Capturing rolled fingerprints without a guide has advantages. These advantages include decreased fingerprint scanner device complexity (no guide components required), and no need to train users to follow the speed of the guide.
Further embodiments, features, and advantages of the present inventions, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.